Near-infrared surface-enhanced Raman spectroscopy of biomedically relevant single molecules on colloidal silver and gold clusters

摘要

Surface-enhanced Raman scattering (SERS) is a phenomenon resulting in strongly increased Raman signals form molecules which have been attached to nanometer sized metallic structures. The technique combines fingerprint capabilities of vibrational spectroscopy and ultra sensitive detection limits. Silver or gold colloidal clusters can provide total enhancement factors of about 14 orders of magnitude for non- resonant Raman scattering at near IR excitation. Since non- resonant near IR photons are used, photodecomposition of the probed molecule is avoided or, at least strongly reduced, and relatively high excitation intensities can be applied. In addition to the Stokes Raman signal, that linearly depends on excitation laser intensity, at excitation intensities higher than approximately 10$+5$/-10$+6$/ W/cm$+2$/ and 10$+7$/ W/cm$+2$/, 'pumped' anti-Stokes Raman scattering and surface enhanced hyper Raman scattering, respectively, can be observed. Both effects can provide a non-linear or two-photon Raman probe where the Raman scattering signal depends quadratically on the excitation laser intensity.